medwireNews: A large observational study shows that pneumococcal serotype is a major determinant of respiratory failure in patients with invasive pneumococcal pneumonia (IPP).

Among 1029 Spanish IPP patients for whom serotype was available, 81.5% of those with serotype 19F developed respiratory failure, as did 65.8% and 65.5% of those with serotype 3 and 19A, respectively. After adjusting for confounders, this equated to a 3.6-, 2.0-, and 2.3-fold increased odds for respiratory failure, respectively.

Other risk factors for respiratory failure, which was diagnosed on arrival in 48.9% of 1258 adults studied, included age over 50 years (odds ratio [OR]=1.63), chronic lung disease (OR=1.54), and chronic heart disease (OR=1.49).

However, the authors, led by Joaquin Burgos (Hospital Universitari Vall d’Hebron, Barcelona, Spain), say “it should be noted that the serotypes, and not the underlying disease, were the main risk factors for respiratory failure in the multivariate analysis.”

These serotypes were also the main risk factors for bilateral radiograph involvement and the need for mechanical ventilation.

Conversely, serotype 1 appeared to have a protective effect against respiratory failure, being associated with a 37% reduced odds for the complication. However, this did not reach statistical significance.

The authors say that the findings “support the hypothesis that specific pneumococcal serotypes play a key role in the development of respiratory failure in patients with pneumococcal pneumonia.”

They add: “These findings are consistent with previous data that associated these serotypes with greatest severity and mortality rates of pneumococcal disease.”

The researchers say that the reasons why some serotypes are more likely to cause respiratory failure are unknown but could be related to the thickness of the bacterial capsule and the ability to adhere to the respiratory epithelium resulting in reduced bacterial clearance from the alveoli.

“This phenomenon could facilitate an excessive inflammatory response that finally leads to cellular damage and lung injury,” they suggest in the European Respiratory Journal.